This is a 5-year proposal, during which the candidate will devote at least 80% of his time to research. He plans to obtain further training in the techniques he will need in the future, such as electron microscopy with Dr. Eick, knockout and knockin mouse production with Dr. Deng, and organ culture with Dr. MacDougall. He plans to spend 2 weeks each with Drs. MacDougall and Deng during year 1, and 4 weeks with Dr. Deng during years 2 and 3. Dr. Feng also plans to attend a series of advanced courses, which include human research training, FDA drug and device approval and drug development, identification of funding sources, writing and presentation skills, statistics and data management, internet and databases, and ethics and scientific conduct. The research plan will test the hypothesis that the Msx1-BMP4 signaling pathway is a key component in epithelial-mesenchymal interactions essential to tooth formation, and that defects in this interaction are likely to lead to tooth agenesis. Aim 1 involves use of selected knockout mouse matings to determine whether Msx1 regulates BMP4 expression by following histologically the expression of reporter genes. Aim 2 involves mating specific pairs of knockout and transgenic mice to determine whether Msx1 and BMP4 are part of the same signaling pathway in tooth formation. Aim 3 will evaluate the relationship of mutations in the Msx1 gene to human familial tooth agenesis, by testing for one specific mutation and possibly evaluation of the entire coding region in affected families. Methodologies include mouse husbandry, histology, DNA analysis of transgenic and null mice, and analysis of DNA from human tooth agenesis patients. Molecular techniques include RT-PCR, in situ hybridization, DNA sequence determination, SSCP (single strand conformational polymorphism), and heteroduplex analysis.